1. Technical Field
The technology described herein relates generally to wireless networking. More particularly, the technology relates to providing additional decoding time for symbols that have been transmitted over a wireless network.
2. Description of the Related Art
Wireless LAN (WLAN) devices are currently being deployed in diverse environments. Some of these environments have large numbers of access points (APs) and non-AP stations in geographically limited areas. In addition, WLAN devices are increasingly required to support a variety of applications such as video, cloud access, and offloading. In particular, video traffic is expected to be the dominant type of traffic in many high efficiency WLAN deployments. With the real-time requirements of some of these applications, WLAN users demand improved performance in delivering their applications, including improved power consumption for battery-operated devices.
A WLAN is being standardized by the IEEE (Institute of Electrical and Electronics Engineers) Part 11 under the name of “Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications.” A series of standards have been adopted as the WLAN evolved, including IEEE Std 802.11™-2012 (March 2012) (hereinafter, IEEE Std 802.11). The IEEE Std 802.11 was subsequently amended by IEEE Std 802.11ae™-2012, IEEE Std 802.11aa™-2012, IEEE Std 802.11ad™-2012, and IEEE Std 802.11ac™-2013 (hereinafter, IEEE 802.11ac).
Recently, an amendment focused on providing a high efficiency (HE) WLAN in high-density scenarios is being developed by the IEEE 802.11ax task group. The 802.11ax amendment focuses on improving metrics that reflect user experience, such as average per station throughput, the 5th percentile of per station throughput of a group of stations, and area throughput. Improvements will be made to support environments such as wireless corporate offices, outdoor hotspots, dense residential apartments, and stadiums.
Included in the focus of the 802.11ax amendment is power-efficient operation of battery-power WLAN devices. Such battery-powered devices may have substantially less processing power than typical line-powered devices.
A frame transmitted in next-generation WLAN technology, such as 802.11ax, may be transmitted using a symbol having a longer duration than symbols used in current WLAN technology such as IEEE 802.11ac. For example, a symbol in an IEEE 802.11ac WLAN may have a symbol duration of 3.2 microseconds (μs), whereas a symbol in an IEEE 802.11ax WLAN may have a symbol duration of 12.8 μs. The symbol in IEEE 802.11ax WLAN may also be transmitted using more subcarriers than the symbol in the IEEE 802.11ac WLAN.
The amount of information encoded into a symbol may be proportional to the duration of the symbol and to the number of subcarriers used to transmit the symbol. Accordingly, a symbol having a duration of 12.8 μs may include four times the information of a symbol having a duration of 3.2 μs. Because the amount of processing time needed to decode a symbol may increase as the amount of information included in the symbol increases, a symbol having a duration of 12.8 μs may take longer to decode than a symbol having a duration of 3.2 μs.
The decoding of a symbol may not begin until the entire symbol has been received.
Space-Time Block Coding (STBC) may also be employed when transmitting information over the WLAN. In STBC, first and second received versions of a symbol may be combined to decode the symbol. The first version may correspond to an encoding of data, and the second version may correspond to an encoding of a complex conjugate of the data.
The first and second received versions of the symbol may be received consecutively. The decoding of a symbol transmitted using STBC may not begin until after the entirety of both versions of the symbol has been received.
A receiving device that receives a frame over the WLAN may be required to transmit a response, such as an Acknowledgement (ACK) frame, within a predetermined time after the end of the received frame. The receiving device may be required to completely decode the received frame before transmitting the response.
When a symbol duration of received frames is increased, STBC is used to encode the received frame, or both, the amount of processing required to decode the final symbol(s) of the received frame may increase. As a result, it may not be possible for some receiving devices, such as battery-powered receiving devices, to complete decoding of the final symbols(s) of the received frame in the time allowed by current WLAN technologies.